The main environmental hazard at Giant Mine is the 237,000 tonnes of highly toxic arsenic trioxide dust stored in 15 underground chambers — there's enough to kill every person in the world. The arsenic trioxide is a byproduct from decades of gold mining.

The mine is close to the shores of pristine Great Slave Lake. Environmentalists and Yellowknife residents alike are worried the dust could leach into the lake.

The site is one of the most contaminated in the country, and it will cost close to $1 billion to clean up.

The federal government plans to freeze the arsenic in place, saying it is too difficult to remove all of the toxic dust. The plan is to use a method similar to how ice rinks are kept frozen — carbon dioxide would be circulated through pipes to keep the dust frozen underground.

27 conditions

In a 233-page report released today, the Mackenzie Valley Review Board says it will recommend the plan be approved as long as 27 conditions are met, including:

shortening the timeframe for dealing with the underground arsenic from perpetuity to 100 years.

facilitating ongoing research in emerging technologies for a permanent solution.

requiring independent reviews of the project every 20 years to evaluate its effectiveness and decide if a better approach can be identified.

treat water on site so that it will be at drinking water standards when it is released.

suggestions for health monitoring in Yellowknife and nearby Dene communities.

divert Baker Creek away from the mine.

create an independent group to oversee the federal government's work.

The board says the measures are required to address the significant adverse environmental impacts and public concern associated with the cleanup.

The federal government's plan to freeze the arsenic in place will go ahead, but the review board says it must be done in a way that the arsenic can be removed later if a better alternative comes up.

It will fall to the federal government to implement most of the measures. It took over responsibility for the cleanup in 1999, when the last owner of the mine went bankrupt.

The report now goes to Aboriginal Affairs and Northern Development Minister Bernard Valcourt, who has the final word on the review.

The minister can also request changes. If the measures are accepted, they will be legally binding.

Fears of contamination to water supply

People who live in Yellowknife say they're worried the arsenic will be a constant threat hanging over future generations.

Many residents are worried that in a worst-case scenario, the arsenic could poison Great Slave Lake, which is one of the biggest lakes in the world.

The condition to shorten the time frame to 100 years is reassuring to some, including Yellowknife Mayor Mark Heyck.

"What it does is it changes the approach I think to the remediation project, in so far as it's not looking at something that's going to be there forever and ever. It's something that has a 100 year window on it," he said.

The report came as welcome news to many groups which have contributed to the five-year-long review.

"It really shifts the way you start to think about the project and the kind of approach the government has taken, to thinking of this as a kind of interim solution, and a lot more work needs to be done. It shifts the onus onto our generation, and maybe the one that comes right after us to work a lot harder to find better solutions and that's a very, very significant shift," said Kevin O'Reilly, who is with a social justice group in Yellowknife called Alternatives North.